Valid Sunday April 30, 2017 to Thursday May 11, 2017
US Hazards Outlook
NWS Climate Prediction Center College Park MD
EDT April 27 2017Synopsis
: Mid-level low pressure is anticipated
across the Central contiguous U.S. during the 3-5 day period, with a forecast
tendency to lift northward, toward and over the Upper Great Lakes region.
Surface low pressure near the Ozarks is forecast to intensify while similarly
lifting northward toward the Great Lakes. Several types of hazards are
predicted to accompany this low pressure system, given both large temperature
differences and the influx of Gulf moisture. Uncertainty is high regarding the
Week-2 circulation and its impacts to the contiguous U.S. Alaska is expected to
experience periodic surface low pressure systems of seasonable strength moving
across the Bering Sea and Gulf of Alaska throughout the outlook period.
Detailed Summary For Sunday April 30
- Thursday May 04:
- Heavy rain across portions of the Central
Plains, the Lower Mississippi Valley, the Northern Plains, the Tennessee
Valley, the Middle Mississippi Valley, the Northeast, the Upper Mississippi
Valley, the Southeast, the Great Lakes, and the Ohio Valley, Sun-Mon, Apr
- Heavy rain across portions of the Southeast, the Lower Mississippi Valley,
and the Tennessee Valley, Tue-Wed, May 2-May 3.
- Severe weather across portions of the Southeast, the Middle Mississippi
Valley, the Lower Mississippi Valley, the Ohio Valley, and the Tennessee
Valley, Sun, Apr 30.
- Flooding possible across portions of the Central Plains, the Lower
Mississippi Valley, the Tennessee Valley, the Great Lakes, the Middle
Mississippi Valley, the Upper Mississippi Valley, the Southern Plains, and the
- Flooding occurring or imminent across portions of the Mid-Atlantic, the
Southern Plains, the Northern Plains, and the Northern Great Basin.
- Flooding likely across portions of the Lower Mississippi Valley, the
Tennessee Valley, the Middle Mississippi Valley, the Mid-Atlantic, the
Southeast, and the Southern Plains.
- High winds across portions of the Central Plains, the Lower Mississippi
Valley, the Northern Plains, the Great Lakes, the Middle Mississippi Valley,
the Upper Mississippi Valley, the Southern Plains, and the Ohio Valley,
Sun-Mon, Apr 30-May 1.
- Much above normal temperatures across portions of the Central Appalachians,
the Tennessee Valley, the Mid-Atlantic, the Southern Appalachians, the Great
Lakes, and the Ohio Valley, Sun, Apr 30.
- Much below normal temperatures across portions of the Southern Rockies, the
Central Rockies, the Southern Plains, the Central Plains, and the Southwest,
Sun, Apr 30.
- Slight risk of much below normal temperatures for portions of the Great
Lakes, the Upper Mississippi Valley, and the Northern Plains, Fri-Sat, May
- Slight risk of much above normal temperatures for portions of the Central
Great Basin, the Northern Plains, the Northern Rockies, the Central Rockies,
California, the Northern Great Basin, the Pacific Northwest, and the Southwest,
Fri-Sat, May 5-May 6.
- Severe Drought across the Tennessee Valley, Hawaii, the Southern
Appalachians, the Southeast, California, and the Southwest.
The primary feature of interest during the 3-7 day
period is an anticipated surface low pressure system which is forecast to track
from the Ozarks northward across the Upper Great Lakes region, before exiting
into eastern Canada. Several hazards are expected to accompany this system. The
first is the potential for severe weather on Apr 30 across the Lower Tennessee
Valley and central Gulf Coast region. The Storm Prediction Center (SPC) expects
favorable vertical wind shear profiles and moderate instability within this
environment for the formation of severe thunderstorms. Another anticipated
hazard with this storm system is heavy rainfall across the east-central and
northeastern CONUS. Northern sections of this area are predicted to receive
between 1.5"-2.5" on Apr 30-May 1, while southern sections are expected to get
between 3"-4". During the subsequent two-day period, May 2-3, the central Gulf
Coast region is predicted to receive an additional 2"-3" of rain. This is due
to the anticipated formation of a warm front over Texas. A third concern with
the original low pressure system is for high winds (30 knots or greater) on the
western side of the storm, from the south-central Great Plains northeastward
across the Midwest and Upper Great Lakes region on Apr 30-May 1. A fourth
potential hazard with this storm system is unseasonably warm air (much
above-normal temperatures) on its eastern side, and unseasonably cold air (much
below-normal temperatures) on its western side. The predicted region of much
above-normal temperatures includes the Mid-Atlantic, central Appalachians, and
Ohio Valley, where temperatures are forecast to range from 12-18 degrees
above-normal on Apr 30. This generally means high's are anticipated to reach
the mid-80's. On the western side of the storm, much below-normal temperatures
are forecast for portions of the central and southern Rockies, and central and
southern Plains on Apr 30. The highlighted area on the map represents an
overlap between expected minimum temperatures in the 20's to low 30's (at or
below freezing), and expected maximum temperatures at or below 50 degrees F.
Flooding is possible, likely, imminent, or occurring across the Carolinas
and southern Virginia, the Lower Ohio Valley/Midwest, the south-central
Mississippi Valley and parts of adjacent states, northern North Dakota, and
parts of Idaho. A cold front which stalled across North Carolina and Tennessee
this past week brought severe storms to the region, rainfall amounts of 2-10",
and flash flooding.
Alaska is forecast to experience periodic low pressure systems tracking
across the Bering Sea and Gulf of Alaska during the 3-7 day period. None of
these systems are expected to be unusually strong for this time of
For Friday May 05 - Thursday May 11:
Substantial uncertainty is apparent
in the wide range of spaghetti map perspectives of the mid-level circulation
over North America in Week-2. Some eastward progression of the circulation
pattern is anticipated, with a trough predicted to approach the East Coast, a
ridge over the Nation's midsection, and another trough entering the western
CONUS. Given the expected progressive pattern, and the forecast of modest
500-hPa height anomalies, limited hazardous impacts can be discerned at this
A slight risk of much above-normal temperatures is forecast for
approximately the western quarter of the CONUS early in the Week-2 period,
in-between an approaching trough to the west, and a departing ridge to the
east. The area of anticipated much above-normal temperatures indicated on the
map is where the GEFS has at least a 20% chance of exceeding the 85th
climatological percentile of maximum temperature. A slight risk of much
below-normal temperatures extends from eastern North Dakota across the Upper
Mississippi Valley, and the western and central Great Lakes region. Here low
temperatures may fall below freezing, while the GEFS supports at least a 20%
chance of being below the 15th climatological percentile of minimum temperature.
According to the U.S. Drought Monitor released on April 27th (using data
through 8 AM EDT, April 25th), coverage of severe, or greater intensity,
drought throughout the CONUS dropped slightly (from 1.44 percent last week to
1.07 percent this week). This is the lowest coverage of D2-D4 drought over the
CONUS since the inception of the U.S. Drought Monitor in
Forecaster: Anthony Artusa
Click here to see a display of the GFS Ensemble Forecasts
Please consult local NWS Forecast Offices for short range forecasts and region-specific information.